Add archive notice

[masih]

Updare readme with archive notice.

Relates to:

• Migrate sei-db into sei-chain as mono repo sei-chain#2457

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.73%. Comparing base (a309e97) to head (0fe43e7).

❌ Your project check has failed because the head coverage (40.73%) is below the target coverage (60.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #124      +/-   ##
==========================================
+ Coverage   40.72%   40.73%   +0.01%     
==========================================
  Files          59       59              
  Lines        7534     7534              
==========================================
+ Hits         3068     3069       +1     
+ Misses       4121     4120       -1     
  Partials      345      345              

see 1 file with indirect coverage changes

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